The present invention relates to a free-flow fluid measurement meter for metering the flow of liquids, particularly milk, and a method for employing such an apparatus.
Free-flow milk meters are known. They provide a valuable tool in monitoring milk production on an individual animal basis. One of their benefits is that milk volume or mass can be measured without batching the milk. Thus, a reading of the milk produced by a cow can be obtained while the milk is being delivered to storage vats directly from the cow.
The measurement of milk produced by animals is a difficult task because the milk being measured is actually a two-phase, gas-liquid system. In modern milking installations, the milk coming from the cow is pumped in a pulsed fashion, permitting the entry of often large amounts of air. Physical properties used to measure milk flow rate, volume, or mass are generally dependent on the percentages of milk and air present. Milk that contains substantial amounts of air, often leads to spurious readings of the parameters used to track the volume, mass, or flow rate of the milk.
In the case of milk flow meters, the formation of froth or foam on top of the air-laden milk can never by avoided completely. In order to minimize the formation of froth or foam and diminish turbulence, the cyclical flow fluctuation caused by the pulsations of the required vacuum apparatus are typically smoothed as much as possible before the milk flows through the measuring chamber of the meter. Both the milk froth or foam and the turbulence cause measuring difficulties by impairing the signal of the sensor used in the milk meter. In addition, most milk meters are subject to milk spray when the milk enters the meter. As a result, during and after use, at least some, if not all, of the meter will be covered by a residue of sprayed milk. An unacceptable film of this milk residue, formed after each milking, must be removed by an adequate cleaning operation. Cleaning is generally effected after milking all members of a herd with the purpose of preventing the growth of microbial organisms.
Typical, free-flow milk meters which can be used to measure the flow rate of milk being delivered and/or the volume and/or mass being measured, without the use of batch measurements are described in U.S, Pat. Nos. 4,452,176, 4,476,719, and 4,346,596, to Hoeflmayer et al., Millar et al. and Diament et al., respectively. All of these meters have complex structures with recessed, partially hidden, surfaces, which make cleaning these meters relatively difficult. Moreover, since they all use direct measurement of a parameter indicative of milk level in the meter, they are dependent on the amount of air present in the milk.
The problems related to milk meters are also encountered in other industrial and laboratory settings. Whenever there is a two-phase, gas-liquid system, measurement of the flow rate, volume, or mass of the liquid in the system is difficult. All these applications require meters that are relatively insensitive to the amount of gas present and which permit easy cleaning.
In what is discussed herein, xe2x80x9cflow ratexe2x80x9d is liquid rate of flow in mass per unit time e.g. kg/min while xe2x80x9ctotal massxe2x80x9d relates to the integration of flow rate over the measurement duration.
The present invention relates to a liquid measuring device, which has been developed, particularly, though not solely, for use as a milk meter which measures the flow and quantity of milk obtained from individual cows in a herd.
It is an object of the present invention to provide a free-flow liquid meter, particularly one for use with milk, that has a simple construction, is cheap to manufacture, and is easy to maintain.
It is a further object of the invention to reduce the air in the liquid being measured, thereby increasing the accuracy of the measurements.
It is an object of the present invention to provide a free-flow liquid metering apparatus that is easy to clean.
It is yet another object of the present invention to provide a method for reducing the effect of entrained gases or air when measuring the flow rate of a free flowing liquid.
The present invention provides a free-flow liquid metering apparatus that consists of a block of sensors, typically electrodes, usually conductivity electrodes, in a specific configuration for precision measurement of the level of liquid in the meter. The measurement sensors are positioned in a helical configuration, a staircase configuration or an otherwise generally stepped configuration. The sensors are positioned between a separation wall containing a slot through which the liquid freely exits and a baffle. The baffle prevents liquid entering the measurement chamber from splashing the electrodes, while freeing entrained gases.
According to one aspect of the present invention, the invention provides a method of measuring flow or volume or mass of a liquid. The method includes the steps of causing the liquid being measured to flow through a slot of generally narrow width but long verticality so that a pool of liquid is maintained upstream of the slot such that the level of the liquid in the pool is a function of the flow rate of the liquid. The flow rate is indicated by measuring the level of liquid in the pool. In addition, the method requires the normalization of the parameter being measured, the parameter typically being conductivity.
According to another aspect of the invention, a baffle is taught where the baffle extends from an upper portion of the free-flow liquid meter""s housing to a lower portion of the meter. The baffle thereby provides a continuous flow surface from the upper portion of the meter""s housing into the lower portion of the housing, preventing splashing on the electrode by the entering liquid.
There is thus provided in accordance with the present invention an apparatus for measuring the flow rate of a liquid tending to froth. The apparatus includes a flow-through housing having an interior and a floor. The housing further includes a separation wall which divides the housing into a measurement chamber and a discharge chamber. The separation wall has a slot in it which allows the liquid to freely flow from the measurement chamber into the discharge chamber. The housing has an inlet communicating with the measurement chamber through which liquid enters the housing. The housing also has an outlet communicating with the discharge chamber through which liquid exits the housing. The apparatus also includes electrical sensor apparatus for sensing the level of the liquid in the measurement chamber. The electrical sensor apparatus includes a reference sensor and a common sensor both positioned proximate to the floor, and a plurality of measurement sensors, These sensors are positioned within the measurement chamber. The measurement sensors are spaced apart in a generally vertical stepped continuum stretching from the floor of the housing to a height substantially equal to the top of the separation wall at predetermined measurement intervals. The apparatus also includes a processing apparatus for evaluating a flow rate, according to a preprogrammed process, based on readings received from the sensors.
Further, in accordance with another embodiment of the measuring apparatus, the processing apparatus includes a microprocessor which receives readings from sensors, and converts the readings to a flow rate by using a look-up table stored in a memory or storage unit. The look-up table correlates the readings to a flow rate. In other embodiments of the measuring apparatus, the processing apparatus includes a microprocessor which receives readings from sensors, and converts the readings to a flow rate by using a function which is stored in a memory or storage unit. The function correlates the readings to a flow rate.
Additionally, in accordance with a preferred embodiment of the measuring apparatus, during use of the processing apparatus, the common and reference sensors measure an electrical parameter of the liquid proximate to the floor of the housing determining a first value, and one or more of the plurality of measurement sensors measures an electrical parameter of the liquid in the one or more measurement sensor""s designated range so as to determine one or more second values. The processing apparatus further includes means for normalizing the electrical parameter measurements of the liquid by evaluating the one or more second values in relation to the first value, obtaining one or more normalized values of the parameter. In addition the processing unit includes a means for converting the one or more normalized values to a flow rate. In some embodiments of the measuring apparatus, the means for normalizing the parameter measurements and the means for converting the one or more normalized values is a microprocessor.
In another preferred embodiment of the measuring apparatus, the plurality of measurement sensors are positioned in a generally stepped configuration, one or more measurement sensors per step. The bottom of the bottom-most measurement sensor is positioned in, and extends from, the floor of the housing. The top of the topmost sensor is positioned substantially co-linear with the uppermost portion of the separation wall. In some embodiments of the measuring apparatus, the plurality of measurement sensors are positioned in a generally helically stepped configuration while in others the plurality of measurement sensors are positioned in a generally linear staircase configuration.
Additionally, in accordance with a preferred embodiment of the measuring apparatus, the sensors are electrodes. In accordance with yet another preferred embodiment of the measuring apparatus, the electrodes are electrodes which measure conductivity.
In another preferred embodiment of the measuring apparatus, the processing apparatus further includes an integrator operative to integrate over time a series of flow rates obtained in accordance with the preprogrammed process, thereby determining the mass of liquid delivered over that period of time. The time over which integration is effected is the duration of the measurements. In other embodiments, the integration is such that the volume of liquid delivered over that period of time is determined.
Additionally, in accordance with a preferred embodiment of the measuring apparatus, the processing apparatus, further includes a microprocessor which receives signals from the sensors, and converts the received signals to a normalized value of a parameter being measured. It then converts the normalized value to a flow rate by using a lookup table stored in a memory or storage unit of the processing apparatus. The look up table relates the normalized value of the measured parameter to a flow rate. In other embodiments of the measuring apparatus, a function is used instead. The function is stored in a memory or storage unit of the processing apparatus. The function relates the normalized value of the measured parameter to a flow rate.
In a preferred embodiment of the measuring apparatus, the apparatus further includes a baffle extending from an upper location of the housing to a lower location of the housing. The baffle has a lower free edge and provides a continuous flow surface from the upper location of the housing into the lower housing portion. The baffle is positioned upstream of the electrical sensor apparatus. It divides the measurement chamber into an inlet volume which receives a generally froth-laden liquid flow from the baffle, and a measurement volume which receives a generally reduced froth content liquid flowing between the lower free edge of the baffle and the floor.
Additionally, in accordance with a preferred embodiment of the measuring apparatus, the processing apparatus evaluates a volumetric flow rate while in other embodiments it evaluates a mass flow rate.
In another aspect of the present invention there is provided an apparatus for measuring the flow of a liquid tending to froth, which includes a flow-through housing which has an inlet formed at an upper location of the housing. The inlet facilitates the inflow into the housing of a liquid having a tendency to froth. The housing also includes a lower housing portion having an interior, a floor, and an outlet formed at a lower location for facilitating free outflow of the liquid from the lower housing portion. The housing also includes a cover configured for placement over the lower portion. A separation wall is positioned in the lower housing portion which divides the lower housing portion into a measurement chamber and a discharge chamber. The wall has a slot permitting free-flow of the liquid from the measurement chamber into the discharge chamber. The housing further includes an electrical sensor apparatus positioned in the measurement chamber for sensing the level of the liquid in the lower housing portion. Finally, the housing includes a baffle extending from an upper location to a lower location of the housing. The baffle has a lower free edge providing a continuous flow surface from the upper location of the housing into the lower housing portion. The baffle is positioned upstream of the electrical sensor apparatus, and divides the measurement chamber into an inlet volume and a measurement volume. The inlet volume receives a generally froth-laden liquid flow from the baffle, and the measurement volume receives a generally reduced froth content liquid flowing between the lower free edge of the baffle and the floor.
Additionally, in accordance with a preferred embodiment of the measuring apparatus, the baffle is formed unitarily with the cover. Removal of the cover removes the division of the lower housing portion into the separate inlet and measurement volumes.
Additionally, in a preferred embodiment of the measuring apparatus, the inlet is formed in the cover for facilitating the inflow into the housing of a liquid having a tendency to froth.
In accordance with another preferred embodiment of the measuring apparatus, the electrical sensor apparatus includes a reference sensor, a common sensor and a plurality of measurement sensors all positioned between the baffle and the separation wall in the measurement chamber. The reference and common sensors are positioned proximate to the floor and the plurality of measurements sensors are positioned vertically and configured to form a generally stepped continuum stretching from the floor of the housing to a height substantially equal to the uppermost portion of the separation wall. The plurality of measurement sensors is in contact with the liquid and measure a parameter with respect to the common sensor. The measured value is normalized using the value of the parameter as measured by the common sensor with reference to the reference sensor. The normalized parameter is convertible to a flow rate by using a processing apparatus according to a preprogrammed process.
Further, in a preferred embodiment of the measuring apparatus, the processing apparatus evaluates a volumetric flow rate, while in other embodiments, the processing apparatus evaluates a mass flow rate.
Additionally, in a preferred embodiment of the measuring apparatus, the electrical sensor apparatus includes a plurality of measurement sensors which are positioned in a generally stepped configuration, with one or more measurement sensor per step. The bottom of the bottom-most measurement sensor is positioned in, and extends from the floor of the housing, and the top of the topmost sensor is positioned substantially co-linear with the uppermost portion of the separation wall. In some embodiments of the measuring apparatus, the plurality of measurement sensors are positioned in a generally helically stepped configuration, while in other embodiments, the plurality of measurement sensors are positioned in a generally linear staircase configuration.
Further, in a preferred embodiment of the measuring apparatus, the electrical sensor apparatus includes a plurality of electrodes. In yet other embodiments, the plurality of electrodes are electrodes which measure conductivity.
In yet another aspect of the present invention there is a method provided for measuring the rate of flow of a liquid including the steps of:
a. passing a liquid through a housing;
b. measuring an electrical parameter of the liquid proximate to the floor of the housing so as to determine a first value;
c. measuring the electrical parameter of the liquid at one or more levels in the housing, the one or more levels including the highest level reached by the liquid so as to determine one or more second value;
d. normalizing the electrical parameter measurement of the liquid measured by evaluating the one or more second value in relation to the first value, thereby to obtain one or more normalized values; and
e. converting the one or more normalized values to a flow rate in accordance with a preprogrammed process.
In yet another preferred embodiment of the method, the method further includes the step of integrating over time the flow rate determined at each measurement time in the converting step, and converting the integrated value to a volume of liquid passing through the housing over the time of the measurements. In another preferred embodiment, the method further includes the step of integrating over time the flow rate determined at each measurement time in the converting step, and converting the integrated value to a mass of liquid passing through the housing over the time of the measurements. The time over which integration is effected is the duration of the measurements.
Additionally, in accordance with a preferred embodiment of the method, the parameter of the liquid being measured is conductivity. In accordance with another preferred embodiment of the method, the liquid being measured is milk.
In yet other embodiments, the method described herein above can be applied to parameters other than electrical parameters.